A method of the type in question is disclosed in Italian patent application BO2005A000360, incorporated here by reference as if set forth in full, and consists in feeding a succession of flat blanks on a first aspirating wheel or roller, immobilizing a first trailing part or portion of the blank located rearwardmost on the aspirating surface (relative to the direction of rotation of the first wheel), and at the same time causing a second leading part or portion of the blank, located forwardmost relative to the aforementioned direction of rotation, to be distanced gradually from the aspirating surface by means of a second aspirating wheel or roller.
The two rollers rotate continuously about respective axes, with the second revolving substantially tangential to the first.
As the trailing portion of the blank advances on the first aspirating roller, the leading portion of the blank is transferred by the second aspirating roller to a third aspirating outfeed roller, rotating continuously and substantially tangential both to the second roller and to the first roller at a folding or pressing station of the machine.
As the first and third rollers rotate, the two aforementioned portions or halves of the blank are brought together gradually, presenting a V formation in profile, to the point of being folded double on passing through the point of tangential association between the first and third aspirating rollers.
Whilst the method briefly outlined above is extremely simple, it nonetheless betrays one notable drawback, in particular at high production speeds.
Importantly, the first and third rollers turn in opposite directions, rotating convergently and at the same peripheral velocity toward their point of mutual tangency.
Similarly, the first and second rollers turn in opposite directions, rotating convergently and at the same peripheral velocity toward a point of mutual tangency where the leading half of the blank separates from the first roller.
It follows therefore that the second and the third roller must rotate in the same direction, and consequently will be turning counter to one another at their point of mutual tangency.
This creates difficulty in transferring, and particularly, in releasing the forwardmost portion of the blank from the second to the third aspirating roller, even though suction means serving the second roller will be deactivated at the moment of transfer.
Moreover, during the step in which the second portion of the blank is folded flat against the first, one end of the blank remains positioned momentarily between the second roller and the third roller and is subjected to a dragging and pulling force.
Besides affecting the part of the blank located at the point of tangency between the second and third rollers, the force in question can also induce plastic deformations in the entire portion of the blank extending from this same point of tangency to the aforementioned folding station.
In practice, the deformations induced by the dragging and pulling force can often lead to an imperfect match between the second and the first portion of the blank, and this also impacts negatively on subsequent welding or sealing steps that the folded nappy/diaper blanks will undergo.